Dual piston internal combustion engine

ABSTRACT

An internal combustion engine (1) comprising at least two cylinders (4,8) meeting to form a combustion space (12) therebetween, a first piston (3) adapted to reciprocate within the first cylinder (4) and a second piston (7) adapted to reciprocate within the second cylinder (8). The two pistons are drivably coupled via a chain drive connecting their respective crankshafts and synchronously move one with respect to the other such that the second piston moves at a frequency haft of that of the first piston. An air/fuel mixture inlet aperture (14) as well as an exhaust aperture (15) are located in the wall of the second cylinder (8) and are opened or closed by the movement of the second piston (7). There is a further exhaust sealing valve (17) such as a rotary disc valve which opens or closes an exhaust port (16) connecting the exhaust aperture (15) to the outside (or exhaust system), the sealing valve (17) closing the exhaust port (16) so as to prevent exhaust gases from re-entering the combustion chamber (12) when the engine is in its intake stroke and when the exhaust aperture (15) is not covered by the second piston (7). The air/fuel mixture enters the combustion chamber (12) through a one-way valve (13), usually a reed valve.

TECHNICAL FIELD

This invention is directed to an improvement in internal combustionengines. In particular this invention is for internal combustion enginescontaining two pistons per cylinder, a primary and a secondary piston,wherein the secondary piston cycles through at a frequency half of thatof the primary piston.

BACKGROUND ART

For a number of years now internal combustion engines have beendeveloped which provide power from fuels such as petrol, diesel and gas,and convert it into a form, usually rotational or linear motion, whichcan then be used to power an enormous range of diverse applications suchas ships, automobiles, motorcycles, electrical generators and evenchainsaws. In its basic form an internal combustion engine convertschemical energy into kinetic energy, by burning of fuels.

A lot of research and development has been expended on internalcombustion engines resulting in a large diversity of designs. Some ofthese include the four-stroke, two-stroke, rotary, and sleeve-valve typeengines. The aim of all this research and development has been toimprove the efficiency of engines and increase the power to weightratio, to make the engines more reliable and robust, and to increasetheir power band range.

The easiest way to increase the power of an engine is to simply increaseits capacity or displacement. However, for an engine of a given sizethere are various other factors which can increase the power. For anengine of a particular size the power available is a function of thepressure within the cylinder during the power stroke, the rate of thepower strokes (commonly known as revolutions per minute), the frictionin the engine and the volumetric efficiency. Therefore, either byincreasing the pressure, increasing the revolutions per minute,increasing the length of the power stroke, decreasing the friction, orincreasing the volumetric efficiency, the power of an engine can beimproved. There are limitations on changing some of the aboveparameters. For example, increasing pressure is limited due to thermalconsiderations and by the ability of the engine to recharge the cylinderwith a fresh air/fuel mixture between power strokes. Increasing therevolutions per minute is also limited due to mechanical constraintssuch as inertial loadings on the valves, bearings, rods and pistons,while increasing the length of the power strokes is limited by inertialloadings on the crankshaft.

This invention is directed to improving the power of an engine for agiven capacity by changing some of the above parameters whichcollectively determine the power of an engine. This invention isdirected towards a four-stroke engine.

DISCLOSURE OF THE INVENTION

Therefore in one form of the invention although this need not be theonly or indeed the broadest form there is proposed an internalcombustion engine comprising of;

two cylinders co-axially aligned and meeting to form a combustion spacetherebetween;

a first piston adapted to reciprocate within the first cylinder;

a second piston adapted to reciprocate within the second cylinder;

the said two pistons being drivably coupled so as to synchronously moveone with respect to the other such that the second piston moves at afrequency half of that of the first piston;

means for providing for an air/fuel mixture inlet through a firstaperture or apertures in the wall of the second cylinder;

means for providing an exhaust outlet through a second aperture orapertures in the wall of the second cylinder;

a timed exhaust sealing valve within the exhaust outlet to effect anopening or closing of the exhaust outlet at a selected time in theoperating cycle of the engine; and

the apertures being positioned so as to be opened or closed by coveringand uncovering of the apertures by the movement of the second piston.

In preference the exhaust sealing valve is a disc-type rotary valve.

This type of exhaust valve arrangement eliminates a popper valve. Thisincreases volumetric efficiency since there is no valve in the way ofthe exhaust gas flow. This also reduces valve stresses and eliminatesvalve hot spotting which occurs in a poppet valve as heat can only bedissipated along the narrow stem of the valve causing it to be thermallystressed. In addition, a poppet valve operates by extending into thecombustion space which requires power when the combustion space is undercompression. The disc-type rotary valve improves mechanical efficiencysince no power is expended working against the compression.

In preference at least a part of the second aperture or apertures is sopositioned on the wall of the second cylinder whereby when the said partis uncovered by the second piston the second piston covers all of theinlet aperture or apertures.

In preference the said part of the second aperture or apertures islocated lower on the wall of the second cylinder than the first apertureor apertures.

In preference the disc-type rotary valve is constructed from a suitablematerial such as ceramic coated plastic although other materials such asAluminium or Titanium may be used. The material to be used may bedictated by the stresses that the engine may be subjected to and theexpected revolutions per minute that the engine may reach as well as thefuel that is to be used since that can have an effect on the operatingtemperature of the engine. Of course, the total cost of production willbe a determining factor in some instances depending on what the proposedapplication of the engine is.

To overcome frictional losses by the disc-type rotary valve rubbingagainst the outside wall of the cylinder, the exhaust portpreferentially protrudes somewhat from the body of the cylinder, theresult being that the disc-type rotary valve only rubs against thatprotrusion. In preference this protrusion is ceramic, although othersuitable materials such as brass may be employed.

The material that the protrusion is to be constructed from will bechosen solely on the basis of its properties. Thus, brass may be apreferred material since it is relatively soft and will not damage thedisc-type rotary valve. But the wear may be minimal since it is thecentifugal force that acts so as to keep the rotary valve in positionand the disc only just touches the protrusion lightly.

Since during the operating cycle there are times when both the first andsecond apertures are uncovered by the second piston, to prevent theexhaust gases flowing through the inlet valve, the air/fuel mixtureinlet further comprising inlet valve that is preferentially a one-wayvalve such as a reed valve, or a rotary disc valve.

The exhaust and inlet apertures are preferentially circular in shapealthough other shapes, such as elliptical can be employed, the shapeonly limited by the mechanical tolerances, such as the rings in thesecond piston.

In preference there is at least one spark plug adapted to ignite theair/fuel mixture in the combustion space, although the engine could bemodified to use diesel fuel which ignites due to compression only, orcould be modified to use more than one spark plug in the combustionspace.

In preference the air/fuel inlet aperture has a construction allowingselective charging of the combustion space, such as stratified charging.

Stratified charging is a means of admitting air to the combustion space,also known as the chamber, so that it is warmed and leans the centrevolume of the chamber. A small tube or a passageway can extend into theexhaust outlet between the second aperture or apertures and the rotarydisc valve. This tube or passageway enters the exhaust outlet in such adirection so as to create a swirl of air around the walls of the exhaustoutlet so that when the air enters the combustion space or chamber it isswirling in a substantially opposite direction to the air/fuel mixturefrom the inlet first aperture or apertures. The majority of the air/fuelmixture stream is directed to substantially adhere to the combustionspace walls and go below the exhaust aperture. However a smallproportion of the air then flows to the exhaust outlet from the smalltube and enters the combustion space above the main intake air/fuelmixture flow swirling at a lower velocity in the opposite direction tothe major air/fuel stream. Therefore it substantially ends up in thecentre of the chamber or combustion space albeit mixed with a percentageof the main air/fuel mixture stream thus leaning it. It is well knownthat a warmer lean mixture will extend the lean flammability limit andtherefore decrease the amount of hydrocarbons left following thecombustion process. The added benefit in the case of this invention isthat the fuel/air mixture stream also acts so as to keep the rotary discvalve and the exhaust outlets cooler.

The small tube or passageway must also have a small valve, such as areed valve, to prevent back flow of gases up the exhaust outlet. Whenthe rotary disc valve closes the exhaust outlet the negative pressure ofthe intake stroke of the engine will draw air through the reed valve andthe tube.

Further upstream of that reed valve is a butterfly valve which can beoperated by a number of means such as a cable, in such a manner as torotate up to 180° when the main throttle has been increased from idle tofull open. Therefore, at idling the air flow is restricted in the smalltube since the butterfly valve is substantially closed. At approximatelyhalf throttle the butterfly valve is fully open and the air flow is atits maximum; this roughly corresponds to the cruising speed of vehicles.However, at full throttle when most power is required the air flowthrough the small tube is restricted by the closure of the butterflyvalve allowing a homogenous mixture in the combustion space. Theaddition of the butterfly valve also means that at idling the air/fuelmixture is not overlean by closure of the butterfly valve.

In preference the second said piston is cylindrical and has a diameterwhich is between 50 to 70 percent of the diameter of the said firstpiston.

In preference the length of the stroke of the said second piston isbetween 25 to 50 percent the length of the stroke of the said firstpiston.

In preference the crown of the first said piston is flat so as tominimise thermal losses, but is not limited to that shape as othershapes may be employed to change various engine characteristics such ascompression ratio.

In preference the crown of the said second piston is conical. Such ashaping helps to perpetuate the swirl of the incoming air/fuel mixturein a wall adhered downward spiral.

In preference the said second piston is connected to a crankshaft whichlies within the piston skirt. In such an arrangement the con rod isconnected away from the piston crown. Although this increases the lengthof the second piston skirt, it moves the position of the second pistoncrankshaft towards the combustion space thereby reducing the size of thediameter of the exhaust disc-type rotary sealing valve and the inletrotary disc valve.

The cooling, lubrication and sealing of the engine may be preferablyaccomplished using any suitable means.

The disc type rotary valves can be preferentially used with both theintake and the exhaust outlets. They are positioned approximately 90° tothe axis of the second piston crank shaft with a 2 to 1 right angledrive on the end of the crank shaft. This cross shaft is linked at a oneend to the exhaust rotary disc valve, or valves in the case of multiplecylinders by either a chain or a tooth belt, while on its other end itis linked to the intake rotary disc valve or valves in the case ofmultiple cylinders. A major advantage of this type of arrangement is thelow requirement for power due to the low speed, and the ability to adaptto in-line engines such as 6 or 4 or V8 to mention a few. For addedbalance the rotary disc valves can be shaped so as to offer acounterbalance. In that case the speed of the crank shaft driving thedisc rotary valves is 4:1 drive as opposed to the 2:1 drive if therotary valves are not of the "butterfly" arrangement. It is to beremembered that reed valves will be quite acceptable for stationaryengines and diesels whilst high performance engines might prefer rotarydisc valves which allow superior gas flow.

It is envisaged that a standard conventional four-stroke engine could beeasily modified to the abovementioned arrangement. This is particularlyattractive as it allows existing engines which are adapted to run onliquid fuels such as petroleum with the addition of tetra ethyl lead(added to offset the problem of detonation and excessive pressure buildup) to be run on unleaded petrol. Although engines can be modified torun on unleaded fuel, this necessitates changing the poppet valves tohardened types in conjunction with hardened seals. By eliminating thepoppet valve unleaded petrol can be used even with an increase incompression pressure.

In a fundamental form, this engine employs the same basic design for thecrankcase and the first piston arrangement as in a conventionalfour-stroke engine. However, instead of the usual poppet valvearrangement as is found on conventional four-stroke engines with onepiston per cylinder, the cylinder head is adapted to use a second pistonin an arrangement where the second piston moves in unison with the mainpiston at half the frequency of the main piston. This second pistonperforms several functions. It increases the compression ratio and actsas a valve arrangement by uncovering the input and output ports whichare apertures in the cylinder. The increase in compression acts toincrease the power output. However, by eliminating the need for poppetvalves not only does the volumetric efficiency increase, but the energyused in a conventional four-stroke engine to drive the valves is nolonger expended. Without the poppet valves, the acoustic properties ofthe engine also change and make the engine quieter. With both pistonsproviding power at the power stroke, the length of the piston strokealso effectively increases.

This type of engine design can be termed an opposed piston six-strokeengine.

BRIEF DESCRIPTION OF THE DRAWINGS

To enable the invention to be fully understood a preferred embodiment ofthe invention will now be described with reference to the followingdrawings where;

FIG. 1 is a cross-section of the engine showing the first (primary)piston and the secondary (Upper) piston when the primary piston is atTop Dead Centre (TDC) and the secondary piston is some 20 degrees afterTDC;

FIG. 2 is the cross-section of the engine as in FIG. 1 but with thefirst piston or crankshaft at approximately 90 degrees rotation;

FIG. 3 is the cross-section of the engine as in FIG. 1 but with thefirst crankshaft at 180 degrees rotation;

FIG. 4 is the cross-section of the engine as in FIG. 1 but with thefirst crankshaft at 270 degrees rotation;

FIG. 5 is the cross-section of the engine as FIG. 1 but with the firstcrankshaft at approximately 360 degrees rotation;

FIG. 6 is the cross-section of the engine as in FIG. 1 but with thefirst crankshaft at 490 degrees rotation;

FIG. 7 is the cross-section of the engine as in FIG. 1 but with thefirst crankshaft at approximately 540 degrees rotation;

FIG. 8 is the cross-section of the engine as in FIG. 1 but with thefirst crankshaft at 630 degrees;

FIG. 9 is the cross-section of the engine as in FIG. 1 but with thefirst crankshaft at 720 degrees rotation;

FIG. 10 is a cross-sectional view of the cylinder head showing theintake and exhaust ports as well as the exhaust rotary disc valve;

FIG. 11 is a cross sectional view of the cylinder head as in FIG. 10 butwith in combination with a small tube/passageway containing a butterflyvalve and small reed valve;

FIG. 12 is an isometric view of one of the preferred embodiments of theengine with a reed inlet valve and a rotary disc exhaust valve;

FIG. 13 is an isometric view of the engine as in FIG. 12 but withcounterbalanced rotary disc-valves used for both the intake and outletvalves;

FIG. 14 is a cross-sectional view of one preferred embodiment of theengine showing a typical oil supply architecture for the upper secondarypiston;

FIG. 15 is a cross-sectional view of the invention when employed on adiesel type engine; and

FIG. 16 is graph showing the relative positions of the primary andsecondary cylinders as a function of a complete cycle.

BEST MODE OF CARRYING OUT THE INVENTION

Turning now to the figures in detail there is shown in FIGS. 1-9 across-sectional view of the engine at various stages through one cycleof operation of one preferred embodiment of the invention. Theembodiment of the invention resides in an engine 1 being a two cylinderopposing engine with an engine block 2, with suitable cooling andlubrication passages (not shown), a first piston 3 within first cylinder4 connected by a first connecting rod 5 to first crankshaft 6, secondpiston 7 located in second cylinder 8 connected by a

second connecting rod 9 to second crankshaft 10. Spark plugs 11 actingin combustion space 12 ignite the air/fuel mixture (not shown) whichenters the combustion space 12 through inlet valve 13, herein a reedvalve, and through an inlet aperture 14 in second cylinder 8. Theexhaust gases (not shown) are expelled through an exhaust aperture 15 insecond cylinder 8 and then through exhaust port 16 which is selectivelyclosable by rotary valve 17. Both the inlet aperture 14 and the exhaustaperture 15 are selectively closable by the second piston 7 whichslidably moves within cylinder 8. The engine may be air cooled via aircooling fins 18. The first crankshaft 6 and second crankshaft 10 aremechanically coupled together by a chain drive (shown in FIGS. 12, 13)and geared so that the second crankshaft 10 rotates at half the angularvelocity of the first crankshaft 6. In this way while the first piston 3completes four strokes the second piston 7 only completes two strokes.The engine inlet aperture 13 and exhaust aperture 14 are covered anduncovered my the motion of the secondary piston.

Turning to the individual stages of the cycle there is shown in FIG. 1the first piston 3 at TDC and the second piston 7 at approximately 20degrees before its BDC. However, the relative position of the secondpiston is not set at 20 degrees relative to the main piston at TDC, forits position can be varied depending on the particular `tuning` of theengine. It has empirically been found that an engine with the secondarypiston at 20 degrees off-set to the main crankshaft at TDC does providegood performance, but different applications may require that positionto be different.

At 0 degrees (all the following rotations will be generally referring tothe position of the first crankshaft unless specifically referred tootherwise) as shown in FIG. 1 the combustion space 12 is fully chargedby an air/fuel mixture (not shown) and is ignited by spark plugs 11. Theburning of the air/fuel mixture increases the pressure in the combustionspace 12 which forces the primary piston 3 downwards through cylinder 4towards its BDC and the secondary piston 7 upwards through cylinder 8 toits TDC. This downward motion causes the first and second crankshafts 6and 10 to rotate, the second crankshaft 10 rotating at half the angularvelocity of crankshaft 6, the two crankshafts mechanically coupled by ageared chain. At the beginning of the cycle the primary piston 3 is atTDC while the secondary piston 7 is 20 degrees before its BDC, thoughthis may not necessarily be the optimum configuration and the relativepositions of the pistons may be varied. However, both the inlet aperture14 and the outlet apertures 15 are closed by the secondary piston whilstthe rotary sealing valve 17 is also closed (though need not be).

FIG. 2 shows the engine 1 half way through completing its first stroke,the power stroke, with the first crankshaft 6 having rotated about 90degrees and the second crankshaft 10 half that, about 45 degrees. Theexhaust sealing valve 17 is closed with the secondary piston 7 at thisstage still covering the inlet aperture 14 and the exhaust aperture 15.The force of the combustion thus still acts on both the primary andsecondary pistons and produces the power of the engine.

FIG. 3 shows the engine when the first crankshaft has now rotatedthrough 180 degrees and the primary piston is at Bottom Dead Centre(BDC). This is therefore the end of the power stroke and the beginningof the exhaust stroke. The secondary crankshaft has only rotated through90 degrees and the secondary piston is still in its upward stroke andhas not yet reached its TDC. The exhaust aperture 15 is so positioned inthe second cylinder 8 that the secondary piston has now started touncover the exhaust aperture 15. The rotary sealing valve 17 now alsohas opened, and exhaust gases 25 can now begin to flow out of thecombustion space 12 through exhaust aperture 15 and exhaust port 16.Since the lowermost part of the exhaust aperture 15 is constructed so asto be slightly lower than the lowermost part of the inlet aperture 14,the inlet aperture 14 has not at this stage been uncovered by secondarypiston 7.

FIG. 4 shows the engine 1 with the first crankshaft 6 at 270 degrees.The second crankshaft 10 has undergone 135 degrees of rotation and boththe inlet aperture 14 and the exhaust aperture 15 are now partlyuncovered by the secondary piston 7. The primary piston is approximatelyhalf-way through its exhaust stroke and acts so as to push out the burntfuel/exhaust gases 25 from the combustion space through the exhaustaperture and out through the exhaust port 16. The inlet valve, being aone-way valve such as a reed valve, does not allow any of the exhaustgases 25 to flow out through the inlet aperture.

FIG. 5 shows the engine when the first crankshaft has rotated through360 degrees and the primary piston is once again at TDC but this time atthe end of the exhaust stroke and at the beginning of the intake stroke.The second crankshaft has now rotated through 180 degrees with thesecondary piston being approximately at 20 degrees before its TDC(because it was 20 degrees before its BDC when the primary piston was atTDC at the beginning of the power stroke). The lower most surface of thesecondary piston is approximately level with the uppermost part of theexhaust aperture to avoid creating any chamber to trap exhaust gases.The exhaust sealing valve 17 has also just about closed the exhaust port16 since most of the exhaust gases 25 would have by now been expelledfrom the combustion chamber 12.

FIG. 6 shows the engine when the first piston is half-way through itsintake stroke with the first crankshaft having rotated through 490degrees. As the first piston 3 moves downwards, there is a suctioneffect produced by the expansion of the combustion chamber and thecombustion space 12 is charged by a fresh air/fuel mixture 26 drawnthrough inlet reed valve 13. During the beginning of the intake strokethe inlet aperture 14 is fully open unlike the case of the conventionalpoppet valve engine thereby resulting in an improved volumetricefficiency. The expelled exhaust gases are prevented from re-enteringthe combustion space 12 by the now closed rotary exhaust sealing valve17. This is important for the movement of the primary piston causes thepressure in the combustion chamber to fall below atmospheric pressureand this sucking motion charges the combustion chamber with freshfuel/air mixture through the inlet valve. If the rotary disc valve werenot present then some of the expelled exhaust gases would also be suckedback into the combustion chamber through the exhaust aperture. Thisobviously would lead to less efficiency since the air/fuel mixture wouldbe mixed with burnt exhaust gases. It is therefore critical that theexhaust port is closed by any suitable means whilst the engine is in theintake stroke so as to avoid the re-entering of the burnt exhaust gasesinto the combustion chamber.

FIG. 7 shows the end of the intake stroke when the first piston 3 is atBDC, the first crankshaft 6 now having rotated through 540 degrees,while the second crankshaft 10 has rotated through 270 degrees and thesecond piston 7 is in its down stroke towards its BDC. The secondarypiston has now partially covered both the inlet and exhaust apertures.The primary piston 3 is now at the beginning of the compression strokeand the rotary disc valve is still covering the exhaust port.

FIG. 8 shows the engine when the primary piston is half-way through itscompression stroke, the first crankshaft having rotated through 630degrees, the second crankshaft having rotated through 315 degrees, thesecondary piston is about half-way through its downward stroke. Thesecondary piston is substantially covering the exhaust and inletapertures. As the first piston 3 moves upwards and the second piston 7moves downwards the combustion space 12 decreases in volume causing theair/fuel mixture to be compressed so that at the end of the compressionstroke, as shown in FIG. 9, the combustion space 12 is substantiallyminimised. FIG. 9 is essentially FIG. 1 with the primary piston 3 beingat TDC and the secondary piston 20 degrees before BDC. At this point thespark plugs 11 ignite the air/fuel mixture and the cycle begins onceagain.

FIG. 10 is a cross-sectional view of the engine through the secondcylinder 8, showing the inlet aperture 14, the exhaust aperture 15, thereed valve 13, and the exhaust rotary valve 17. The inlet aperture 14may preferentially include a dividing part 18 which acts to impart ahigher velocity swirl to the air/fuel mixture 26 around the outer areasof the combustion space 12 and a lower velocity to the inside areas orthe combustion chamber thereby aiding in the combustion process. Howeverit is to be understood that the engine is not limited to a particularair/fuel charging means, and various features may be changed to improvethe combustion process, such as fuel injection, or using a rotary discinlet valve.

FIG. 11 shows the cross sectional view of the engine as in FIG. 10showing the second cylinder 8, the inlet aperture 14, the exhaustaperture 15, the reed valve 13, the exhaust rotary valve 17, and thecombustion chamber 12. However, FIG. 11 also includes an additionalfeature that may be employed to enhance the operation of this engine.That is, there is a stratified charge tube 40 containing a small reedvalve 41, butterfly valve 42 the stratified charge tube allowingair/fuel mixture 43 to enter the combustion space in a swirling motion44, and in an opposite direction to the main air/fuel mixture 26. It isto be understood however that this is only an additional feature thatmay be employed to improve the homogeneity of the air/fuel mixture anddoes not need to be used to perform the invention.

FIG. 12 is an isometric view of the engine showing the first crankshaft6, the second crankshaft 10, the chain drive 20 connecting the saidfirst crankshaft 6 to the said second crankshaft 10, the one way-inletvalve being a reed valve 13, the rotary exhaust sealing valve 17, theexhaust port 16 and the exhaust bearing holder cap (manifold) 21.

The rotary sealing valve is held in position by a compression spring(not shown) which acts so as to push the rotary valve onto against theexhaust port. To aid in this and to reduce frictional losses the exhaustport may include a slight protrusion. The exhaust protrusion istherefore the portion of the exhaust port that may be in contact withthe rotary sealing disc valve which may be simply a flat plate so shapedto allow the exhaust port to be opened or closed depending on therotation of the first and second crankshafts. It is to be understoodthat the rotary sealing valve 17 acts to prevent the back flow of theexhaust gases into the combustion chamber through the intake part of theengine cycle. The rotary disc valve may be driven directly by the secondcrankshaft 10 so that its opening and closing of the exhaust port can befinely tuned. The shape of the rotary disc valve 17 may also be variedaccording to the particular requirement. Thus, although in FIG. 12 therotary disc valve 17 is shown as a flat plate with at least two straightedges 30, those straight edge passing across the exhaust port 16 so asto open and close it, the shape of the edges may be varied and mayinclude but not be limited to curved edges which act to quicker coverand uncover the exhaust port.

The positioning and size of the inlet aperture 14 and the exhaustaperture 15 can all be varied to suit particular requirements. In FIGS.1-9 the inlet aperture 14 is shown as being substantially opposite theexhaust aperture 15. However, this is only for schematic purposes andone of the more appropriate position is shown in FIG. 10 and 11, wherethe relative position of the apertures is such that there centre axisare substantially at 90 degrees to each other. The apertures may also beplaced at different vertical positions in the cylinder wall with respectto the combustion space thus making the valve timing and compressionratio variable. It is to be also understood that there may be more thanone inlet or exhaust aperture, similarly to the multi-valve conventionalpoppet engines that are well known.

FIG. 13 is an isometric view of the engine as in FIG. 12 but with boththe inlet valve and the exhaust valve being rotary sealing valves. Thisrequires there to be an additional rotational driving mechanism (notshown) that opens and closes the inlet valve at the appropriate part ofthe engine cycle.

FIG. 13 further shows the rotary valves being counter-balanced tominimise vibrational effects within the engine. The actual shape of therotary valves isnot relevant, what is critical is that they cover anduncover the inlet and exhaust ports at the right time in the cycle. Thusin the case of the exhaust aperture the exhaust port must besubstantially opened through the exhaust cycle, that is when the firstcrankshaft is in the 180 to 360 degrees rotation, and it must besubstantially closed through the intake cycle, that is 360 to 540degrees. Of course, because the intake cycle follows the exhaust cycleit is impossible to instantly close the port at 360 degrees, and this iswhere the shape of the rotary disc valve can play a significant part. Itmay be even advantageous to have the exhaust port uncovered at thebeginning of the intake cycle or otherwise, however, these are factsthat may be changed when the engine is being tuned for differentoperating requirements. Thus, as discussed below, a racing engine willbe tuned differently to a normal engine.

It is to be understood that the relative size of the sealing valves isunimportant and various sizes may be employed to suit various enginedesigns. In addition when the sealing valves are of the counter balancedconstruction as shown here then the drive ratio of the valves may be 4:1as compared with the main crankshaft speed.

FIG. 14 is a typical example of an oil system for the secondary or upperpiston 7. The cylinder 8 within which the piston slides usually includesa sleeve 60 which is manufactured from a hard-wearing material such ascast-iron. Through this sleeve there is an oil pressure feed 50 which,feeds oil to the secondary piston and cylinder as well as to the slide51 of the scotch-yoke of the upper piston. The upper piston includes atleast one (but preferentially more) scraper ring 52 which acts so as toscrape the oil off the sleeves 60. The oil (not shown) is extracted bythe use of a ring-shaped cavity 53 outside of the cast sleeve 60. Thescraper ring 52 is substantially level with the scraper ring when thesecondary piston is at its TDC. A series of holes are drilled throughthe sleeve as well as the secondary piston. An extractor pump (notshown) draws oil gathered by the scraper ring 52 as well as smallquantities of air from the inside of the piston and return it to thesump or oil holding tank (not shown).

FIG. 15 shows the invention when used for a diesel type engine. Thesetypes of engines usually work without the aid of a spark plug and relyon the fact that diesel fuel will ignite when subjected to a particularpressure. Generally diesel engines compress the air and the fuel isinjected into already pressurised air. Since it is therefore the totalvolume into which the air/fuel mixture is compressed that is importantthe combustion space 12 may be designed to be smaller by suitableconstruction,. In this particular case, the combustion chamber is madesmaller by making the pistons substantially covering the respectivecylinders and leaving only a small combustion space therebetween. Thefuel is introduced into the chamber via injectors 70, and there may be afurther secondary combustion chamber 71 which aids in the efficientoperation of the engine.

FIG. 16 is a graph showing the relative positions of the primary andsecondary piston when the secondary piston as tuned so as to be 20degrees BDC whilst the primary piston is at TDC. In addition, there isshown on the graph the relative timings of the opening and closing ofboth the intake and the exhaust ports. The y-axis refers to a particularvolume in cubic centimetres, due to empirical research, particularly amotorbike engine. However, it is not intended to limit this invention toany particular size or to any relative size of the primary to thesecondary piston or stroke. This graph is intended to show only onetypical example of an engine which was found to satisfactorily work.

Thus there are a number of advantages in an engine the subject of thisinvention as compared with conventional internal combustion engines thatoperate one piston per cylinder. The loads on the first crankshaft orthe main crankshaft of an engine constructed as taught by this inventionare reduced overall as compared with those in a standard engine duringthe compression and expansion strokes. Thus the loads at TDC compressionwould be marginally smaller, at 10 degrees ATDC they would be greater,at 20 degrees ATDC would be about equivalent, whilst thereafter theywould be smaller. The reduction of the load should result in lessfriction in the main crankshaft assembly. Thus assuming that thefrictional characteristics of this engine as compared to a standard oneare about the same, the reduction of the load should lead to greatermechanical efficiency.

A further advantage of this invention is that the head should absorbless heat than a standard head. The significant area being the exhaust.In conventional engines, the poppet exhaust valve is directly in thepath of gas flow and there is considerable turbulence as the exhaustgasses pass out of the cylinder. The temperature of the poppet valve maythus reach over 1000 degrees Centigrade. The flow out of the head asdisclosed in this invention is less turbulent as there is not metalprotrusion in the gas flow. The resulting gas flow is thus lessturbulent, and looses less heat than a convention engine. This has thefurther advantage in that the light up time for the catalytic converterfound in most engines these days is reduced. A further advantage thatmay occur is that due to less turbulence, the head absorbs less heat andthe incoming charge density of the air/fuel mixture may be greater. Thereduction of turbulence also leads to less pumping losses.

Another advantage of this invention is that the exhaust port iscontinuously being further exposed (enlarged) this continuing nearlytowards the end of the stroke when the rotary disk comes into action.This may be compared with the standard engine poppet valve which startsreducing the gas flow at around 600 degrees of the stroke cycle, atwhich point its maximum, lift is reached. This invention enables themaximum exhaust port area to occur at 710 degrees. Furthermore, thenature of the exhaust opening also tends to reduce any acoustical noiselevel. The larger opening for the exhaust port allows more use of thekinetic energy up the column of the exhausts gasses and creates anegative pressure in the combustion chamber.

In racing engines where excess fuel consumption and excess hydrocarbonsare not an issue this kinetic energy may be used in a similar manner totwo-stroke engines. To enhance this process, the closing of the diskvalve should be ideally left to later in the cycle, say approximately at70 degrees ATDC on the intake stroke. In this instance, a portion of theintake mixture follows the exhaust column and may fill the first severalcentimetres of the exhaust pipe. Thus in a multi-inlet port engine theremay be one intake port positioned substantially opposite an exhaust portin the upper cylinder wall so as to direct an intake stream across thecombustion chamber at the exhaust port whilst the other intake ports aredirected away from the exhaust port down the cylinder.

To add more kinetic energy to the process the exhaust should be openearlier at approximately 460 degrees. But also to widen the window ofopportunity between when the intake port is closed and the exhaust portis closed, at approximately 250 to 300 degrees instead of 250 to 270degrees. The trailing edge of the rotary disk should be timed to openthe exhaust port again At approximately 240 degrees, this allowing thereverse pressure pulse from the two stroke style exhaust to ram thefirst 50 to 75 mm (2-3 inches) of intake mixture in the exhaust pipeback into the combustion chamber before the exhaust port is closed. Anengine of this design would not idle very well but should produce goodpower at higher rotation speeds.

A yet further advantage in this engine is that there is a residualpressure in the cylinder before the exhaust valve is opened. In thestandard engine work is expanded by the cam to unseat the exhaust valveagainst this pressure (that pressure usually being of the order of 50-70pounds per square inch). However, in the engine the subject of thisinvention, this pressure is utilized to do work via the upper piston. Ifthe upper piston has an area of approximately 3000 square millimetres(4.5 inches square), this results in a force of up to 400 hundredpounds, although 300-340 is more likely because of lower pressures dueto the greater expansion stroke. However, the combustion has beenshifted slightly so as to occur later in the cycle so the actualphysical properties are yet to be determined accurately.

Turning now to the reed valve, its use confers an advantage in thatintake occurs whenever pressures or the kinetic energy of intake orexhaust column dictate. But also the reed valve causes the gas velocityto be greater than normal at low throttle settings promoting good swirlwhich further aids in atomising the fuel. This therefore acts somewhatas a pseudo second venturi.

Referring now to the crankshaft motions, in prior art the upper pistonreaches its TDC well in advance of the main piston. This inventionhowever teaches that even if the stroke is variable the upper pistondoes not reach its TDC before the main piston. A further additionalfeature of this engine that may be used and is used so as to minimisethe space requirements (specifically the vertical extent caused by thesecond piston) is that the head faces away from the main piston crown,os in another embodiment may be a scotch yoke. Both of these imparts adifferent motion to the upper piston than has been taught in other priorart and results in the piston acceleration being slower than in the headas described above or a scotch yoke. Thus mechanically it is easier toachieve a TDC of the upper piston after the main piston has reached TDC.

There are three main reasons for desiring the main piston to reach TDCprior to the secondary piston. Firstly this allows more advantageoustiming as fas as the opening the ports and closing the intake. Secondlythis maintains a longer period of relatively constant (or close to)volume during which combustion can occur. Thirdly it places peakcylinder pressure later in the expansion phase.

The most advantageous timing would of course vary for different enginedesigns. Thus one could vary the TDC coincidence from 1 to 40 degrees,depending on the particular engine and particular application.

The above description is not intended to limit the invention to thatdescription only. Various changes may be made to the above embodimentsso illustrated and described without deviating from the spirit of thisinvention.

I claim:
 1. An internal combustion engine comprising of;two cylindersco-axially aligned and meeting to form a combustion space therebetween;a first piston adapted to reciprocate within the first cylinder; asecond piston adapted to reciprocate within the second cylinder; the twopistons being drivably coupled so as to synchronously move one withrespect to the other such that the second piston moves at a frequencyhalf of that of the first piston; means for providing for an air/fuelmixture inlet through a first aperture or apertures in the wall of thesecond cylinder; means for providing an exhaust outlet through a secondaperture or apertures in the wall of the second cylinder; a timedexhaust sealing valve within the exhaust outlet to effect an opening orclosing of the exhaust outlet at a selected time in the operating cycleof the engine; and the apertures being positioned so as to be opened orclosed by covering and uncovering of the apertures by the movement ofthe second piston.
 2. An internal combustion engine as in claim 1wherein the exhaust sealing valve is a disc-type rotary valve.
 3. Aninternal combustion engine as in claim 1 wherein at least a part of thesecond aperture or apertures is so positioned on the wall of the secondcylinder whereby when the part is uncovered by the second piston thesecond piston covers all of the inlet aperture or apertures.
 4. Aninternal combustion engine as in claim 3 wherein the part of the secondaperture or apertures is located lower on the wall of the secondcylinder than the first aperture or apertures.
 5. An internal combustionengine as in claim 1 wherein the exhaust outlet includes a protrusionwhich protrudes somewhat from the body of the cylinder resulting thedisc-type rotary valve only contacting against that protrusion.
 6. Aninternal combustion engine as in claim 5 wherein the protrusion isceramic, although other suitable materials such as brass may beemployed.
 7. An internal combustion engine as in claim 1 wherein theair-fuel mixture inlet further comprises a one-way inlet valve.
 8. Aninternal combustion engine as in claim 1 wherein the inlet valve is areed valve.
 9. An internal combustion engine as in claim 1 wherein theexhaust and inlet apertures are substantially circular in shape.
 10. Aninternal combustion engine as in claim 1 wherein the exhaust and inletapertures are substantially non-circular in shape, such as but notlimited to elliptical.
 11. An internal combustion engine as in claim 1wherein there is at least one spark plug adapted to ignite the air/fuelmixture in the combustion space.
 12. An internal combustion engine as inclaim 1 wherein the engine is adapted to use diesel fuel which ignitesdue to compression.
 13. An internal combustion engine as in claim 1wherein there is a secondary air/fuel inlet aperture so positioned toeffect the air/fuel to enter the combustion space in a swirling motionand thereby act so as to cause a preferential charging of the combustionspace, whereby the motion of the air/fuel mixture from the secondaryair/fuel aperture is in a direction substantially different to thatentering the combustion chamber through the main air/fuel inletaperture.
 14. An internal combustion engine as in claim 1 wherein thesecond piston is cylindrical and has a diameter which is between 50 to70 percent of the diameter of the first piston.
 15. An internalcombustion engine as in claim 1 wherein the length of the stroke of thesecond piston is between 25 to 50 percent the length of the stroke ofthe first piston.
 16. An internal combustion engine as in claim 1wherein the crown of the first piston is substantially flat so as tominimise thermal losses.
 17. An internal combustion engine as in any oneof claim 1 wherein the crown of the piston is shaped to affect thecompression ratio.
 18. An internal combustion engine as in claim 1wherein the crown of the second piston is substantially conical.
 19. Aninternal combustion engine as in claim 1 wherein the first piston isconnected to a first crankshaft, the second piston is connected to asecond crankshaft, the first and the second crankshaft drivably coupledto each other whereby the second crankshaft rotates at an angularvelocity half that of the first crankshaft.
 20. An internal combustionengine as in claim 1 wherein the second piston is connected to acrankshaft which lies within the second piston skirt.
 21. An internalcombustion engine as in claim 20 wherein the second piston is connectedto the crankshaft via a con-rod which faces away from the crown of thesecond piston.
 22. An internal combustion engine as in claim 1 whereinthe cooling of the engine is accomplished by conventional means such aswater-cooling or air-cooling.
 23. An internal combustion engine as inclaim 1 wherein the disc type rotary valves can be used with both theinlet and the exhaust outlets.
 24. An internal combustion engine as inclaim 19 wherein the exhaust rotary disc valve is substantially openthrough most of the rotation of the first crankshaft of between 180 to360 degrees, the exhaust stroke.
 25. An internal combustion engine as inclaim 19 wherein the exhaust rotary disc valve is substantially closedthrough most of the rotation of the first crankshaft of between 360 to540 degrees, the intake stroke.
 26. An internal combustion engine as inclaim 19 wherein the maximum exhaust port area occurs substantially at710 degrees of rotation of the first crankshaft.
 27. An internalcombustion engine as in claim 19 wherein the rotary sealing valve isfully closed at 70 degrees rotation of the first crankshaft.
 28. Aninternal combustion engine as in claim 19 wherein the second cylindercauses the inlet aperture to be closed at 250 degrees rotation of thefirst crankshaft.
 29. An internal combustion engine as in claim 19wherein the second cylinder causes the inlet aperture to be open whenthe first crankshaft rotation is between 250 to 700 degrees.